Displacement control feedback apparatus and method

Abstract

A feedback apparatus according to the present invention elastically interconnects the swashplate of a variable displacement hydraulic unit with the valve spool of a hydraulic unit displacement control, and is constructed such that a predetermined spring preload force is developed. A feedback spring extends along the valve spool and is surrounded by an elongated housing coupled with the swashplate. Axially movable spring guides are interposed between opposite ends of the spring and a flange formed at each end of the housing. A suitable spacer is positioned between the spring and at least one of the spring guides to compress the spring to a length representative of the desired preload.

I claim: 
     
       1. A feedback apparatus in a displacement control for a variable displacement hydraulic unit having a positionable swashplate, the displacement control including a valve spool axially movable within a valve body, the axial position of the valve spool operating to position the swashplate, the feedback apparatus comprising: an elongated housing coupled with the swashplate and slidably mounted on the valve spool, the housing having an axially extending housing interior and spaced apart housing ends;   a pair of spring guides guided for axial movement and constrained between a pair of spaced stops on the valve spool;   spring means within the housing interior for biasing the spring guides outwardly into abutting relation with the opposite ends of the housing, the spring means being adapted to apply a predetermined level of preload force for outwardly biasing the spring guides into engagement with the stops on the valve spool such that positioning of the swashplate by the displacement control causes axial movement of the coupled housing along the valve spool to force one of the spring guides against a stop to cause axial movement of the valve spool;   means for varying the level of preload force developed by the spring;   each of the housing ends having an opening for receiving the valve spool, the openings in the housing ends defining an inwardly extending flange at each end thereof; each spring guide means comprising a sleeve coaxial with the valve spool and having an outwardly extending collar; and   the inwardly extending flange at each end of the housing defining an opening therein, the outwardly extending collar on each spring guide engaging the flange to prevent movement of the spring guide through the opening when the spring guide sleeve is coaxially aligned with the valve spool.   
     
     
       2. The feedback apparatus of claim 14 in which the outwardly extending collar on each spring guide includes flats formed thereon to permit movement of the spring guide through the opening in the housing during assembly. 
     
     
       3. In a displacement control for adjusting the position of a swashplate in a variable displacement hydraulic unit, the displacement control having a fluid metering valve including a valve spool axially moveable within a valve body, the axial position of the valve spool operating to position the swashplate, a feedback apparatus constrained between spaced apart stops on the valve spool and comprising: an elongated housing coupled with the swashplate and guided for axial movement along the valve spool, the housing having opposite ends with an opening formed therein for receiving the valve spool;   a spring mounted concentric with the valve spool and disposed between the opposite housing ends, the spring having a predetermined length whereby positioning of the spring within the housing generates a preload force against the opposite housing ends;   a pair of spring guides slidably mounted on..the valve spool between the opposite ends of the spring and the opposite housing ends and associated one each with a stop on the valve spool, the stops begin positioned on the valve spool such that positioning of the swashplate by the displacement control causes axial movement of the coupled housing along the valve spool to force one of the spring guides against the stop to cause axial movement of the valve spool.   
     
     
       4. The feedback apparatus of claim 3 including means for varying the level of preload force generated when the spring is captured between the opposite housing ends. 
     
     
       5. A method for interconnecting a positionable swashplate in a variable displacement hydraulic unit with a swashplate displacement control by means of a feedback spring having a predetermined preload, the method including the steps of: providing a feedback spring having two spaced ends;   applying a fixed load representative of the predetermined preload to the spring, whereby application of the fixed load causes axial deflection of the spring;   measuring the distance between the two ends of the spring when the spring is deflected under the fixed load, the fixed load being removed after the measurement;   providing an elongated housing having spaced apart ends, the housing ends being spaced apart a known distance;   providing a first spring guide in the housing, with the spring guide seated at one end of the housing;   providing a removable insert between the first spring guide and an adjacent end of the spring, the insert having a thickness representative of the difference between the measured distance between the two ends of the spring when the spring is deflected and the distance between the spaced apart housing ends;   compressing the spring in the housing;   providing a second spring guide in the housing to retain the spring therewithin in a compressed state.   
     
     
       6. The method of claim 5 comprising the further step of providing a sleeve on said spring guide which has an outwardly extending collar which is adapted to permit movement of the spring guide through an opening in said housing.